1. Field of the Invention
The present invention generally relates to a method of displaying a plurality of images that are similar to each other, and relates to a memory medium having a program embodied therein for displaying such a plurality of images.
2. Description of the Related Art
An increase in CPU speed together with increases in memory volumes of main/secondary memory devices have made it easier to treat image data. Further, widespread use of the Internet and digital cameras or the like have made it possible to transfer image data to personal computers or the like quite easily, resulting in a large volume of image data flooding around us in everyday life. Against this background, there is a need for a scheme that allows a user to search for a desired image from a massive amount of image data.
A conventional scheme for image search typically conducts a search by using attribute information after manually attaching the attribute information to images. This scheme, however, cannot cope with a rapid increase of image data. In recent years, an effort has been directed to a study on a scheme that automatically extracts image features such as color histograms, textures, and shapes from image data, and searches for an image resembling a specified image by using the extracted image features. This study has proven to be a success.
Such image search schemes include a scheme that extracts image features from images in advance, and extracts image features from an image specified as a search key, followed by comparing the image features of the specified image with the image features of other images to find resembling images. This scheme can show a reasonably good performance when the number of image features is small, but suffers a decrease in processing speed as the number of image features increases.
In terms of graphical interface, a typical image search system presents search-result images by arranging them in a row in a descending order of similarity. This kind of display lacks presentation of relationships between images that are gauged quantitatively at an image pattern level. Similarity measures of images may not reflect the user's intention of his/her search, so that the search results are merely one of the factors to be used in the user's decision making. There is a need, therefore, for interface that can assist a user to organize the search results. In particular, a resembling image search is, by its definition, conducted with ambiguity existing in the user's search request, and the user tends to try and see as many images as possible. In such a situation, many search results need to be presented to the user.
In consideration of this, an interface that presents to the user as many search results as possible and asks for the user's judgment is disclosed in “A User Interface Visualizing Feature Space for Content-Based Image Retrieval,” Technical Report of IEICE, IE98-204. This interface presents a complete listing of search results in such an organized fashion as to allow a user to intuitively understand underlining treads of the search results. In detail, images obtained as search results are subjected to principal component analysis, and image features obtained by the analysis are mapped into a 2-dimensinal-display space to present the search results. Since the principal component analysis is applied only to the search-result images rather than to all the images of the database, the number of feature dimensions is significantly lower, achieving compression of information. Further, the search-result images can be presented by more accurately reflecting a nature of image-set distribution and by more widely spreading the search-result images, thereby allowing the user to grasp underlining treads of the search-result images.
In the field of a relating endeavor, a visual interaction scheme is disclosed in “Visual Interaction for Exploration in Information Space of Documents,” Journal of JSSST, Vol. 13. This scheme introduces an idea of dynamic updating of visualized results in a visual classification technique where the updating is performed in response to a user operation, and the visual classification is given by arranging a large number of documents and keywords based on their mutual relationships. Presentation of search results in this visual interaction scheme arranges documents close to each other in a 2-dimensional or 3-dimensinal space if these documents resemble each other according to the similarity measure of the documents. Such a similarity measure is obtained, for example, by using indexes.
The scheme disclosed in “A User Interface Visualizing Feature Space for Content-Based Image Retrieval,” Technical Report of IEICE, IE98-204 has a problem in that principal analysis cannot be carried out when image features cannot be represented by vector data or when image similarity between images cannot be represented by a linear function.
The scheme disclosed in “Visual Interaction for Exploration in Information Space of Documents,” Journal of JSSST, Vol. 13 has a drawback in that a large amount of computation becomes necessary when the number of keywords becomes large, which makes a processing time lengthy, thereby making it difficult for a user to grasp a nature of the interactively presented visual information.
Accordingly, there is a need for a resembling image search scheme that can display search-result images at high speed according to similarity measures obtained in a feature space even when image features cannot be represented by vector data or even when image similarity cannot be represented by a linear function.